1. Field of the Invention
The present invention relates to a road data maintenance system, and more particularly, to a system capable of constantly updating road data possessed by an information center.
2. Description of the Related Art
Recently, various techniques associated with ITS (Intelligent Transport Systems) have been proposed and have become increasingly popular. One example of ITS is a vehicle information system in which a number of vehicles are connected with an information center via communication means so that data can be transferred between them. In such a system, each vehicle receives from the information center various types of useful information regarding the vehicle use. It is also proposed that the information center collects information useful for its operation from the vehicles.
In this type of system, map data, especially road data contained in a map, has an important role. The information center is provided with a database of road information including the latest road data. For example, the following uses for road data has been considered.
(a) Road data itself: Road data is sent to a vehicle which uses the received road data to navigate the vehicle; PA1 (b) Guiding route: The information center prepares a guiding route sends it to the vehicle. The vehicle uses the guiding route for navigation. Preferably, the vehicle first sends to the information center various conditions including a start location and a destination, and other conditions required to determine a route; PA1 (c) Traffic information: Traffic information regarding, for example, traffic congestion is prepared and sent to the vehicle; and PA1 (d) Destination information: Information concerning a destination of the vehicle is provided.
It is not easy for the vehicle alone to acquire the latest data, or to process a large amount of data. In the above system, it is expected that up-to-date, comprehensive road data can be handled by the information center.
Since it is desired for the information center to always store the latest road data, the road data is maintained as needed. During the data maintenance, new road data which is not stored in the information center (referred to as "unpossessed (unstored) road data" hereinafter) is added to the existing road data stored in the center (referred to as "possessed (stored) road data" hereinafter).
For example, when a new road (unpossessed road) is constructed which may include new bridges or tunnels, or when the contour of a road may change permanently or temporarily due to road construction, the road data possessed by the information center needs to be maintained using the contour of the unpossessed road or the location of intersections.
In a known system, new road data is prepared and forwarded to the information center by a cartographer who makes a map using air photos and field survey results. Since map making is not carried out frequently, the provision of new road data is delayed by the month so that the information center can receive it only sometime after the opening of the new road.
Alternatively, a special survey may be carried out before a new road is opened if the opening date is known in advance, but there still remains a need for an easier method of obtaining the road data.
As described above, there is a substantial delay in providing the unpossessed road data to the information center in the known technique. Thus, the real time acquisition of the latest information and maintenance of data by the information center have been prohibited.
Japanese Patent Laid-Open Publication No. Hei8-271272 discloses a navigation system in which an on-vehicle navigation system includes a CD-ROM (Compact Disc Read Only Memory) which stores road data. If a vehicle runs on a road which is not stored in the CD-ROM, data concerning this road will be stored in another memory other than the CD-ROM. As such, the navigation system can utilize the latest road information for route guidance. In this technique, however, the new road is detected exclusively for one vehicle. The system does not allow the maintenance of road data in the information center, which is required in the ITS, nor the new road data is available for other vehicles.
In addition, there is still a room for improving the reliability of newly detected road data in the above technique. Namely, the current position detecting means used for detecting the data may generate a large error. Also, the system may use the CD-ROM of an old version, generating less reliable road data. As the data becomes less reliable, various features including the navigation feature may operate improperly.